The present invention relates to a rock bolt and method of forming a rock bolt particularly but not exclusively, a rock bolt for use with a resin anchor.
To install a rock bolt in a mine wall a hole is firstly drilled in the wall and a chemical or resin mixture inserted in the hole. The bolt may then be inserted and is preferably rotated during insertion to mix the resin. To enhance mixing, the bolt may be provided with suitable thread form. In the event the diameter of the hole is greater than desired, a mixing device, such as a wire spirally wrapped along the length of the bolt may be provided. Alternatively, a paddle section may be provided by stamping the bolt.
A disadvantage associated with forming the paddle section is that substantive compressive load needs to be applied and the resultant stresses plastically deform the bolt axially as well as sidewardly of the bolt. The sideward displacement of material in the bolt is minimal and control of the shape of the paddle section is difficult to achieve.
It is an object of the invention to provide an improved rock bolt which includes a paddle section.
In accordance with the invention, there is provided a bolt including a paddle section formed by deforming a portion of the bolt through application of an eccentric shear force.
Preferably the paddle section includes two paddle portions projecting substantially parallel to a centre line bisecting the bolt, the portions being displaced to opposite sides of the bolt and the centre line.
Preferably, the bolt includes an expandable shell mounted to the paddle section, the shell including wedges adapted to be forced outwardly, by axial movement of the paddle portions therethrough, to lock the bolt against a wall of a bolt hole.
Preferably, a plurality of paddle sections are formed along the extent of the bolt.
In another aspect, there is provided a method of forming a bolt including applying an eccentric shear force to the bolt to deform a portion of the bolt laterally hereof and thereby produce a paddle section.
Preferably, the method includes applying an eccentric shear force from opposed sides of the bolt, parallel to and on opposite sides of a centre line bisecting the bolt.